1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier or a laser beam printer, provided with attachment devices such as an automatic document feeder for automatically feeding original documents to an exposure position, or a sorter for sorting and collating the recording sheets after image formation.
2. Description of the Prior Art
There is already known an image forming apparatus such as a copier, used in combination with attachment devices such as an automatic document feeder for feeding original documents to an exposure position, and a sorter for sorting and collating the recording sheets after image formation.
Certain automatic document feeders to be used in combination with a two-side copier can handle both originals having images on one side only and originals having images on both sides, and in such automatic document feeders the original document is circulated to an original inserting tray and is inverted by an inverting device in the circulating path to achieve automatic copying of both sides of the original document. However, in case of making plural two-side copies, for example n copies, from an original document, such circulating system has to transport the original document 2n times to the exposure station, thus causing damage in the original document and requiring an extremely long time for the copying operation.
Also certain automatic document feeders are provided with different original inserting trays for one-side copying and two-side copying. In such feeders the operator may insert the original document in a wrong tray, thus inducing an erroneous copying operation.
Also in case a sorter is attached to a copier, the operator often does not notice an abnormality in the density or position of the image on the recording sheet, occuring in the course of a copying operation with the sorter and can find such abnormality only when the recording sheets are taken out from the sorter. Such abnormality is less apt to be noticed particularly when the recording sheets are kept with their faces downward in the sorter.
Furthermore, in such image forming apparatus with an automatic document feeder, the operator often overlooks an abnormality of inclined image or partially lacking image caused by a defective feeding of the original document.
Such situation, if not attended immediately, is undesirable in terms of economy and efficiency of the office jobs.
However, in such situation, the operator has to remove the defective recording sheets one by one from the storage bins of the sorter and has to suitably dispose of the removed recording sheets.
In case of copying important documents, such defective copies cannot be merely thrown into a trash box but have to be brought for example to a shredder.